Signaling system



oct. s, 1925. 1,556,311

J.DAWDSON,JR l

SIGNALING SYSTEM Filed Dec. 2?:I 1920 Patented Oct. 6, 1925.

1 UNITED ,STATES y 1,556,311 :PATENT OFFICE.

JOHN DAVIDSON, JR., oF TRENTON, NEW JERSEY, yAssIcrNoR TO AMERICAN4"TELE- 4 PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

sIGNALINe sYs'IInu.`

Application niedvnecember 23, 19:50.y seriai No. 432,783.

To all whom-#May concern.' Beit known that'I, J oHN DAvIDsoN, Jr.,

residing at Trenton, in the county of Mercer and State ofNew Jersey,have invented certain Improvements in a Signaling System, of which thefollowing is a specification. n v vThis invention relates to signalingsystems and particularly to an arrangement whereby the signalingapparatus associated lwith a telephone circuitmay be -controlled .bymeans of a modulatedhigh frequency current.

It has been customary heretofore to operate the signaling apparatusassociated with telephone circuits by lmeans of currents of relativelyAlow frequencies, lthat isto say, currents varying from approximately 16to 133 cycles vper second. With the development of long distancetelephony and teleg-l raphy, especially through the invention of vtheso-called carrier systems, it'vhas been found that thesignaling-frequencies `heretofore used could well be used for revenueproducing purposes, as for instance for alternating current telegraph.The voice frequency range (which is not, available for additionalrevenue producing channels) was thereforey proposed for .signaling sincetalking and signaling are notdone-at vthe same p time. It hasaccordingly been foundy desirable to use signaling currentsof higherfrequencies'so asv to take them voutside the frange of frequencies ofthe proposed telegraph channels butat the Sametime to keep the frequencyof the telephone signaling current ywithin ycertain prescribed limits.

It is they object of this invention to provide an arrangement whereby amodulated `high frequency signaling current may be impressed upon theline circuit andtransmitted thereover as such high frequency Ycurrentand'to vdemodulate the said high frequency current'using its lowfrequency component for the operation of the terminal signalingapparatus.

1 Other and further ob'ects of this invention will be apparent rom thefollowing description when read in connection with lator.) 3 andfl itswhich may be of any well-known type. Bridged `across the terminating endof the line circuit L1 is a relay R.1 which is adapted to respond to lowfrequency ringing current impressed thereon by the operation of therelay R2 and tol cause thereby the operation of the relay R3 which, inturn, vlights the line signal l. Another relay R,v associated withthesleeve of the ack J 1 is adapted to f' lopen the .circuit of therelay R1 and also to extinguish the line signal lamp l Vwhen the plug-PLis insertedin jack 1. "Also, by .the act of inserting a plug in saidjack, the f l relay `R5 Lis operatedwhich, in t'urn, roperates relay R6whereby filaments of the vacuum tubes associated with the oscillator 2and the modulator 3 are heated thereby setting in operation the saidoscillator, and putting the modulator in condition to function properly.The operation of relay R, alsor conu y nects with .the modulator circuita source of v135 cycle current whereby the unmodulated oscillations, forexample, V2000 cycles set up Vby the said oscillatorr 2, may bemodulated.

Bridged across the -lineV circuit L1 at Athe points 4, 4Lk is aVrelaynR7 which, by means of vind'uctance 5 and capacity 6, is lmaderesponsive tothe low Vfrequency current impressed upon the line circuitbythe operator whenever thev ringing key of the cord circuit associatedwith the plugP1 is operated but is not responsive to highv frequencyoscillations received over the linev Ll from a distant point. The`operation of relay lR7 grounds thevvwinding of relay Rs which causestheoperation fof relay R, and im- .pr'esses-upon-the line circuit L,.themodul.lated lhigh frequency oscillations which, as

previously stated, wererset up bythe moduwhich, for example, representsa band resulting from the modulation of the 2000 cycle current with 13,5cycle current. These high frequency oscillations are impressed upon thedetector 10 and the resulting low freq'uency `current will cause theoperation of a sensitive relay R9 which,'in turn, releases the' normallyoperated, slow-release relay Rw. This slow-releaserelay in turn controlsthey operation of the relay R2 which;

associated apparatus. Bridged across the line circuit L1v at the.Ipoints7, 7 is a circuit`8'which i'sjcoupled with-the input circuit 9 ofa vacuum tube ldetector 10; VThe circuits 8 and 9 `are tuned for thereception of the modulated frequency effects the application of the lowfrequency current., of, for example, approximately 20 cycles, to therelay R1 which isy bridged across the switchboard end of the line L1;

Having in mind the foregoing description of the parts comprising thearrangement shown in Fig. 1 in which this invention re'- sides, thenature of the invention will be more clearly understood fromthefollowing description of the mode of operation of this 'arrangementLet it be'assumed that the operator at A desires to signal the operatorat the vdistant end of the line Lrpand1 thaty the apparatus connected'with the distant end of this line isv substantially that shown inthefigure. llien the operator `ai; A inserts the plug P1 in the jack J1land depresses the ringing' key of the cord circuit associated withvtheplug P1, low frequency ringing current will be impressed 'across theline L1. This results in the operation of relay R7', since theimpedance. of the path through this relay is ylow for current of thisfrequency. Relay R7 will be operated thereby operating relay R8 and thearmatures of the latter relay will connect theli'ne side of line L1 withthe contact-s withv which the source of modulated high frequencysignaling current is connected. Furthermore, when the plug P1 isinserted in'jacll Jrelay R4 will be operated, thereby removing thebridged relay R1 from the line, and also relay R5 will be operatedwhich, in turn, causes the operation of relay R6. When relay R6 isoperated current will flow from battery B1 ythroughthe filamentsof theoscillator 2 and the modulator 3 and at the same timethrough the closingof the outer contact of relayR6 135 cycle current will be impressed uponthe circuit of the modulator by means ofv a vtransformer The oscillator'2 may be of any wellknown type or arrangement and as is well known,such circuits' will begin to oscillate as soon asthe filament of thevacuum tube connected therewith is heated. Accordingly the unmodulatedoscillations from the oscillator circuit 2 will vbe modulated by the 135cycle current which is also impressed upon the input side of the.modulator 3 andy the resulting modulated oscillations willbeimpressedup'on 'the line circuit connected with the'inner contacts ofrelay R8. The resultantV modulated vhigh frequency oscillations will beimpressed upon'the line L1 andV in turn will be impressed upon acircuitat the distant end of the said line circuit similar to thecircuit shown in the figure.

The action of these high frequency oscillations at the distant end willbe thesame as would-take place if similar modulated high frequencykoscillations were impressed 'upon the distant end and were received bythe terminal circuit shown in the figure.

Let it be assumed that such modulated high frequency oscillations havebeen impressed upon the line L1 at thedistant end and that the plug P1of the cord circuit at A has not been inserted in jack J '1. rlliemodulated high frequency oscillations will be impressed upon the circuit8 and those oscillations falling within the frequency range of the tunedcircuit 9 will be impressed thereon and in turn will be detected bymeans of the detector 10. The 135 cycle component of VYthe highfrequency `wave, which appears in the output side of detector 10 willenergize relay R9 which will open the circuit of relay R15 allowing thisarmature to drop back. This act results in' the grounding of a windingof relay R21 connected withthe line circuit L1 and'ZO cycle ringingcurrent will be in'ipressedupon the relay R-l which is bridged' acrossthe tip and ring side of the switchboard end of the line L1. The relayR3 will 'accordingly be operated, locking up'over Va contactof relay R4Land also lighting the line signal lamp 1.

When the operator at A takes up the'call by inserting the plug P.1 in'the jack J1, current fromthe battery B, of the sleeve of the plug willoperate relays and' R5. 'The operation of relay R4 results inextinguishing the light of the lamp 1 and also opening the circuit ofthe bridged relay R1. The operation of relay R5 results in settinginoperation the oscillator and causing'thereby the production /ofmodulated oscillations, but in view of the fact that relay R7 remainsinoperative, relay RS will accordingly remain inoperative and the highVfrequency oscillations from the output side of the modulator 3 will not'be impressed upon the line L1.

It will be seen that my invention comprises an arrangement for ringingover telephone circuits by means of modulated high frequencyoscillations which are transmitted from one end and detected ordemodulated at the other end of the circuit and' using the low frequencycomponent for theoperation of a sensitive; relay which in turn applieslowfrequency current for the operationof the signals in the 4mannerwhich is well understood. Y i

In the form in which this invention has been disclosed in Fig. 1 notonly is the unmodulated lcarrier frequency transmitted but also both ofthe side bands arising from the superpositionfthereon of the 135 cyclemodulating current. However, by the insertion lin the circuit betweenthe modulator and the relay 4RS of suitable filters of any well knowntype as shown in Fig. 1a, only one side blandfmay be transmitted whichmay be detectedI by means of a suitable tuned circuit connected with thecircuit of the detector 10.v KBy adjusting the lilters, which may be ofthe band type, yboth the carrier and one band may be transmitted.

Although this invention has been disclosed as embodied in a particularform for arrangement of parts, it is to be understood it is capable ofembodiment in other and different forms without departing from thespirit and scope of the appended claims.

What is claimed is:

1. In a signaling system the combination of a line circuit, `a cordcircuit having a source of ringing current connected thereto, a sourceof high frequency oscillations, a source of low frequency variations,means to modulate said high frequency oscillations by the said lowfrequency variations, and means controlled by the connection of the saidcord circuit with the said line circuit to effect the modulation of thesaid high frequency oscillations by the said low frequency variations.

2. In a signaling system the combination of a line circuit, a cordcircuit having a source of ringing current connected thereto, a sourceof high frequency oscillations, a source of low frequency variations,means to modulate said high frequency oscillations by the said lowfrequency variations, and means controlled by the application of the lowfrequency ringing current to the said line circuit to cause the saidmodulated high frequency'oscillations to be impressed upon the saidcircuit.

3. In a signaling system the combination of a line circuit, a cordcircuit adapted for connection with the said line circuit and having asource of low frequency ringing current associated therewith, a sourceof modulated .high frequency oscillations, and means responsive to theapplication of low frequency ringing current to the said line to controlthe Connection of the said source vof modulated high frequencyoscillations to the said line circuit.

4. In a signaling circuit characterized by the transmission thereover ofmodulated high frequency waves, the combination with a line circuit of aline relay and signal associated therewith, a detector adapted toldemodulate the said waves, a second relay trolled by the said cordcircuit to impress the said high frequency oscillations uponl the saidline circuit, a detector circuit adapted to have impressed thereon highfrequency oscillations received over the said line circuit from itsopposite end, andmeans connected with the output side of the saiddetector circuit for controlling the operation of the line signalconnected with the said line circuit. r

6. In a signaling system the method for operating the line relayassociated with long telephone circuits which consists in generatinghigh frequency oscillations, modulating the said high frequencyoscillations with low frequency variations, impressing the saidmodulated oscillations upon the line circuit,

receiving the said modulated oscillations at the opposite end of theline circuit by a detector circuit tuned to reception frequency, andimpressing the detected low frequency component upon a relay adapted tocontrol the operation of the line signal by means of low frequencycurrent.

7 In a signaling circuit, the combination with a line circuit of aterminal circuit having a link circuit associated therewith, the saidterminal circuit comprising means for generating a modulated highfrequency wave, means for receiving and detecting a modulated highfrequency wave, and means controlled by the connection of the said linkcircuit to the said terminal circuit to disconnect the said receivingand' detecting means from the said line circuit when the said generatingmeans is connected therewith.

8. In a communication system comprising a low frequency communicationcircuit adapted to be connected with a carrier frequency transmissioncircuit, the said carrier requency circuit having means associatedtherewith for generating a carrier frequency current modulated by anintermediate frequency signaling current, the method of signalin whichconsists in connecting the said low requency communication circuit withthe said transmission circuit controlling thereby the generation of thehigh frequency carrier current and its modulation by the intermediatefrequency current, and applying low frequency signaling current from thesaid low frequency circuit to the Vhigh frequency circuit to control theapplication of the modulated carrier current to the said high frequencytransmission circuit.

In testimony whereof, I have signed'my name to this specification this21st day of December 1920. s

JOHN DAVIDSON, JR.

